/*
 * ElementUnionLabel.java March 2011
 *
 * Copyright (C) 2011, Niall Gallagher <niallg@users.sf.net>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

package wx.xml.simpleframework.xml.core;

import java.lang.annotation.Annotation;

import wx.xml.simpleframework.xml.Element;
import wx.xml.simpleframework.xml.ElementUnion;
import wx.xml.simpleframework.xml.strategy.Type;
import wx.xml.simpleframework.xml.stream.Format;

/**
 * The <code>ElementUnionLabel</code> is an adapter for an internal
 * label. Each annotation within the union can be acquired by type
 * so that deserialization can dynamically switch the converter used.
 * Each union label can be used in place of any other, this means
 * that regardless of which union is matched it can be used.
 * <p>
 * Each instance of this <code>Label</code> is given the union and
 * the primary label it represents. This allows the label extract each
 * other label within the union group. The <code>Converter</code>
 * created by this can therefore acquire any label instance required.
 *
 * @author Niall Gallagher
 * @see wx.xml.simpleframework.xml.ElementUnion
 */
class ElementUnionLabel extends TemplateLabel {

    /**
     * This is used to extract the individual unions in the group.
     */
    private GroupExtractor extractor;

    /**
     * This is the union associated with this label instance.
     */
    private ElementUnion union;

    /**
     * This is the expression that is associated with this label.
     */
    private Expression path;

    /**
     * This is the contact that this label is associated with.
     */
    private Contact contact;

    /**
     * This is the label that this acts as an adapter to.
     */
    private Label label;

    /**
     * Constructor for the <code>ElementUnionLabel</code> object. This
     * is given the union this represents as well as the individual
     * element it will act as an adapter for. This allows the union
     * label to acquire any other label within the group.
     *
     * @param contact this is the contact associated with the union
     * @param union   this is the union annotation this represents
     * @param element this is the individual annotation used
     * @param format  this is the format used to style the union
     */
    public ElementUnionLabel(Contact contact, ElementUnion union, Element element, Format format) throws Exception {
        this.extractor = new GroupExtractor(contact, union, format);
        this.label = new ElementLabel(contact, element, format);
        this.contact = contact;
        this.union = union;
    }

    /**
     * This is used to determine if this label is a union. If this
     * is true then this label represents a number of labels and
     * is simply a wrapper for these labels.
     *
     * @return this returns true if the label represents a union
     */
    @Override
    public boolean isUnion() {
        return true;
    }

    /**
     * This is used to acquire the contact object for this label. The
     * contact retrieved can be used to set any object or primitive that
     * has been deserialized, and can also be used to acquire values to
     * be serialized in the case of object persistence. All contacts
     * that are retrieved from this method will be accessible.
     *
     * @return returns the field that this label is representing
     */
    @Override
    public Contact getContact() {
        return contact;
    }

    /**
     * This acquires the annotation associated with this label. This
     * is typically the annotation acquired from the field or method.
     * However, in the case of unions this will return the actual
     * annotation within the union group that this represents.
     *
     * @return this returns the annotation that this represents
     */
    public Annotation getAnnotation() {
        return label.getAnnotation();
    }

    /**
     * This is used to acquire the <code>Label</code> that the type
     * provided is represented by. Typically this will return the
     * same instance. However, in the case of unions this will
     * look for an individual label to match the type provided.
     *
     * @param type this is the type to acquire the label for
     * @return this returns the label represented by this type
     */
    @Override
    public Label getLabel(Class type) throws Exception {
        Type contact = getContact();

        if (!extractor.isValid(type)) {
            throw new UnionException(this, "No type matches %s in %s for %s", type, union, contact);
        }
        return extractor.getLabel(type);
    }

    /**
     * This is used to acquire the <code>Type</code> that the type
     * provided is represented by. Typically this will return the
     * field or method represented by the label. However, in the
     * case of unions this will provide an override type.
     *
     * @param type this is the class to acquire the type for
     * @return this returns the type represented by this class
     */
    public Type getType(Class type) throws Exception {
        Type contact = getContact();

        if (!extractor.isValid(type)) {
            throw new UnionException(this, "No type matches %s in %s for %s", type, union, contact);
        }
        if (extractor.isDeclared(type)) {
            return new OverrideType(contact, type);
        }
        return contact;
    }

    /**
     * This method returns a <code>Converter</code> which can be used to
     * convert an XML node into an object value and vice versa. The
     * converter requires only the context object in order to perform
     * serialization or deserialization of the provided XML node.
     *
     * @param context this is the context object for the serialization
     * @return this returns an object that is used for conversion
     */
    @Override
    public Converter getConverter(Context context) throws Exception {
        Expression expression = getExpression();
        Type       type       = getContact();

        if (type == null) {
            throw new UnionException(this, "Union %s was not declared on a field or method", label);
        }
        return new CompositeUnion(context, extractor, expression, type);
    }

    /**
     * This returns a <code>Collection</code> of element names. This
     * will typically contain both the name and path of the label.
     * However, if this is a union it can contain many names and
     * paths. This method should never return null.
     *
     * @return this returns the names of each of the elements
     */
    @Override
    public String[] getNames() throws Exception {
        return extractor.getNames();
    }

    /**
     * This returns a <code>Collection</code> of element paths. This
     * will typically contain only the path of the label, which is
     * composed using the <code>Path</code> annotation and the name
     * of the label. However, if this is a union it can contain many
     * paths. This method should never return null.
     *
     * @return this returns the names of each of the elements
     */
    @Override
    public String[] getPaths() throws Exception {
        return extractor.getPaths();
    }

    /**
     * This is used to provide a configured empty value used when the
     * annotated value is null. This ensures that XML can be created
     * with required details regardless of whether values are null or
     * not. It also provides a means for sensible default values.
     *
     * @param context this is the context object for the serialization
     * @return this returns the string to use for default values
     */
    @Override
    public Object getEmpty(Context context) throws Exception {
        return label.getEmpty(context);
    }

    /**
     * This is used to acquire the <code>Decorator</code> for this.
     * A decorator is an object that adds various details to the
     * node without changing the overall structure of the node. For
     * example comments and namespaces can be added to the node with
     * a decorator as they do not affect the deserialization.
     *
     * @return this returns the decorator associated with this
     */
    public Decorator getDecorator() throws Exception {
        return label.getDecorator();
    }

    /**
     * This returns the dependent type for the annotation. This type
     * is the type other than the annotated field or method type that
     * the label depends on. For the <code>ElementList</code> and
     * the <code>ElementArray</code> this is the component type that
     * is deserialized individually and inserted into the container.
     *
     * @return this is the type that the annotation depends on
     */
    @Override
    public Type getDependent() throws Exception {
        return label.getDependent();
    }

    /**
     * This is used to either provide the entry value provided within
     * the annotation or compute a entry value. If the entry string
     * is not provided the the entry value is calculated as the type
     * of primitive the object is as a simplified class name.
     *
     * @return this returns the name of the XML entry element used
     */
    @Override
    public String getEntry() throws Exception {
        return label.getEntry();
    }

    /**
     * This is used to acquire the name of the element or attribute
     * that is used by the class schema. The name is determined by
     * checking for an override within the annotation. If it contains
     * a name then that is used, if however the annotation does not
     * specify a name the the field or method name is used instead.
     *
     * @return returns the name that is used for the XML property
     */
    public String getName() throws Exception {
        return label.getName();
    }

    /**
     * This is used to acquire the path of the element or attribute
     * that is used by the class schema. The path is determined by
     * acquiring the XPath expression and appending the name of the
     * label to form a fully qualified path.
     *
     * @return returns the path that is used for the XML property
     */
    public String getPath() throws Exception {
        return label.getPath();
    }

    /**
     * This method is used to return an XPath expression that is
     * used to represent the position of this label. If there is no
     * XPath expression associated with this then an empty path is
     * returned. This will never return a null expression.
     *
     * @return the XPath expression identifying the location
     */
    public Expression getExpression() throws Exception {
        if (path == null) {
            path = label.getExpression();
        }
        return path;
    }

    /**
     * This is used to acquire the name of the element or attribute
     * as taken from the annotation. If the element or attribute
     * explicitly specifies a name then that name is used for the
     * XML element or attribute used. If however no overriding name
     * is provided then the method or field is used for the name.
     *
     * @return returns the name of the annotation for the contact
     */
    @Override
    public String getOverride() {
        return label.getOverride();
    }

    /**
     * This acts as a convenience method used to determine the type of
     * the field this represents. This is used when an object is written
     * to XML. It determines whether a <code>class</code> attribute
     * is required within the serialized XML element, that is, if the
     * class returned by this is different from the actual value of the
     * object to be serialized then that type needs to be remembered.
     *
     * @return this returns the type of the field class
     */
    public Class getType() {
        return label.getType();
    }

    /**
     * This is used to determine if the label is a collection. If the
     * label represents a collection then any original assignment to
     * the field or method can be written to without the need to
     * create a new collection. This allows obscure collections to be
     * used and also allows initial entries to be maintained.
     *
     * @return true if the label represents a collection value
     */
    @Override
    public boolean isCollection() {
        return label.isCollection();
    }

    /**
     * This is used to determine whether the annotation requires it
     * and its children to be written as a CDATA block. This is done
     * when a primitive or other such element requires a text value
     * and that value needs to be encapsulated within a CDATA block.
     *
     * @return this returns true if the element requires CDATA
     */
    @Override
    public boolean isData() {
        return label.isData();
    }

    /**
     * This is used to determine whether the label represents an
     * inline XML entity. The <code>ElementList</code> annotation
     * and the <code>Text</code> annotation represent inline
     * items. This means that they contain no containing element
     * and so can not specify overrides or special attributes.
     *
     * @return this returns true if the annotation is inline
     */
    @Override
    public boolean isInline() {
        return label.isInline();
    }

    /**
     * Determines whether the XML attribute or element is required.
     * This ensures that if an XML element is missing from a document
     * that deserialization can continue. Also, in the process of
     * serialization, if a value is null it does not need to be
     * written to the resulting XML document.
     *
     * @return true if the label represents a some required data
     */
    public boolean isRequired() {
        return label.isRequired();
    }

    /**
     * This is used to describe the annotation and method or field
     * that this label represents. This is used to provide error
     * messages that can be used to debug issues that occur when
     * processing a method. This will provide enough information
     * such that the problem can be isolated correctly.
     *
     * @return this returns a string representation of the label
     */
    public String toString() {
        return label.toString();
    }
}
